1 Field of the Invention
The present invention relates to a magnetic tape cassette having improved tape travel stability at the recording and reproducing station within the cassette.
2. Description of the Prior Art
With the recent trend toward small and light-weight tape cassette recorders, the development of small magnetic tape cassettes therefor and tapes which can be recorded and reproduced at high density for a long period of time has been stressed. To meet such a demand tapes such as the C-120, C-180 and the like have been put into practical use. In addition, the surface of the recording medium must have a mirror finish to accomodate higher density recordings.
A well-known miniaturized magnetic tape cassette of this type is shown in FIG. 1, and comprises a hollow plastic case 1 including an upper member 1a and a lower member 1b secured together by fixing means 1c. A tape travel route is defined by elements disposed within the case, including a pair of reels 2, 3, a fixed guide pin 4, a rotary guide roller 5, a fixed guide pin 6, a pressing pad 7, a fixed guide pin 8, a rotary guide roller 9, a fixed guide pin 10, and flat guide plates 11 inserted between the inner sides of the upper and lower members 1a, 1b and the reels 2, 3. A tape T wound onto the supply reel 2 is fed over the pressing pad 7, which urges the tape against a recording and reproducing head (not shown), to the take-up reel 3 while both edges of the tape are restrained from lateral movement by the guide plates 11.
When the recording and reproducing head is inserted through a receiving window 13, the magnetic tape passing through a recording and reproducing station 12 is pushed towards a shield plate 14 disposed behind the pressing pad 7 against the force of a biasing spring, whereby the tape is guided over the upright outer surfaces of the fixed pins 6 and 8 disposed upstream and downstream of the station 12.
Such a prior art cassette suffers from the following disadvantages, however:
(1) Since the plastic case members and internal elements are assembled by screws, ultrasonic adhesion, or the like, strains easily occur, and as a consequence the tape travel stability is impaired which results in unstable contact between the tape and the recording and reproducing head.
(2) Since the tape contact surfaces of the fixed guide pins 6, 8 are machined to have a vertical orientation, if the tape becomes laterally displaced in its travel path upstream or downstream of the pins, there is no way to correct such displacement resulting in a correspondingly displaced or inferior contact between the tape and the recording and reproducing head. Further, such displacement tends to increase as the thickness of the magnetic tape is decreased.
(3) The unstable or displaced contact described in paragraphs (1) and (2) above is often induced by changes in the mounting position of the cassette as between horizontal and vertical cassette decks, which produces differences in the electromagnetic conversion and output frequency characteristics.